Prime Video works fine with this device, but Netflix is sub-par compared to Apple TV 4K.
Netflix decides what format to select based on the audio/video capabilities of the player. It will only play 4K/UHD through this device if the 4K Firestick is plugged into an HDMI port that supports 4K at 50/60 Hz. On my TV, a 2015 Vizio M-55C2, there is only one such HDMI port, HDMI 5. This port won't upscale from below 720p, so my SD content and devices are unplayable on my TV without moving the HDMI cable to port 1 or 2. Apple TV 4K is happy with 4K at 30Hz, so no cable moving needed.
Netflix will also not play Dolby Atmos content through the Firestick at all. I have a very nice AVR - Denon X4400H - that all my TV devices connect to and it reports its capabilities correctly. I don't know why Netflix can't see Dolby Atmos support on the 4K Firestick, and neither does Netflix. They said it's an Amazon problem.
The Bluetooth remote is kind of a joke. Apple uses Bluetooth too, but it also put an IR receiver in the Apple TV so you can use a programmable remote like the Logitech Harmony to control the device. Amazon, unfortunately, doesn't appreciate why people want to use programmable remotes for A/V systems to control all their devices.
Amazon's hardware products always suffer from poor execution and bizarre design approaches, so I shouldn't have been surprised: I have a Kindle reader I don't use and an original Fire TV that I got for CalMan that doesn't work all that well either.
I only got this thing because Amazon's Prime Video app for the Apple TV 4K didn't support any audio better than 2 channel stereo for the longest time. They finally fixed that, but they still have too little content for Dolby Atmos; the new Jack Ryan series is pretty much the only show they have. I have a Dolby Atmos setup with 12 speakers - four in the ceiling - so I want to be able to play Atmos content whenever it's available.
Amazon shuts the door on Atmos through Netflix, so I returned the Firestick 4K. I suspect this is fixable with a firmware update, but I don't have any need to wait for one since I already have a better alternative.